In the production of a highly integrated semiconductor element, usually, a conductive thin film such as a metal film as a conductive wiring material and an interlayer dielectric film for insulation between conductive thin films are formed on an element such as a silicon wafer, and after that, a photoresist is homogeneously applied to the surface thereof to provide a photosensitive layer, which is subjected to selective exposure and development to form a desired resist pattern. Next, the interlayer dielectric film is subjected to the dry etching treatment using the resist pattern as a mask, thereby forming a desired pattern on the thin film. Then the resist pattern and residue generated by the dry etching treatment (hereinafter referred to as “dry etching residue”) are completely removed by ashing with oxygen plasma, a cleaning liquid or the like. Such a series of processes is generally carried out.
Recently, the design rule has been more and more shrunken, and RC delay has controlled the limit of high-speed processing. For this reason, the conductive wiring material has been changed from aluminum to copper which has lower electric resistance, and with this, the interlayer dielectric film has been changed from a silicon dioxide film to a low-dielectric-constant interlayer dielectric film (a film having a dielectric constant of lower than 3; hereinafter referred to as a “low-dielectric-constant interlayer dielectric film”). Further, in order to prevent diffusion of copper in the interlayer dielectric film, copper is covered with a metal such as tantalum and tantalum nitride (hereinafter referred to as a “barrier metal”) and an insulating film such as silicon nitride and silicon carbide (hereinafter referred to as a “barrier dielectric film”). In addition, between the photoresist and the interlayer dielectric film, a film having the function of planarization by being filled in a gap such as concavity and convexity, a groove or the like in a base element, the function to absorb radiation reflected from the element and the function to maintain the shape of the interlayer dielectric film at the time of dry etching to facilitate precise microfabrication, tends to be more often used. As such a film, for example, an organosiloxane thin film including a light-absorbing compound (hereinafter referred to as an “organosiloxane-based thin film”) is used. Further, in the case of forming a pattern of 0.2 μm or less, when a resist having a film thickness of 1 μm is used, the aspect ratio of the pattern (the ratio obtained by dividing the resist film thickness by the resist line width) becomes too high, causing problems such as collapse of the pattern. In order to solve the problems, a hard mask method, in which: a Ti-based or Si-based film (hereinafter referred to as a “hard mask”) is inserted between a film which is desired to be actually formed a pattern and a resist film; a resist pattern is transferred to the hard mask by dry etching; and after that, the pattern is transferred to the film which is desired to be actually formed the pattern by dry etching, using the hard mask as an etching mask, may be used. In this method, the gas to be used for etching the hard mask may be different from the gas to be used for etching the film which is desired to be actually formed the pattern. When etching the hard mask, a gas which doesn't etch the resist can be selected, and when etching the actual film, a gas which doesn't etch the hard mask can be selected. Therefore, the method is advantageous on the point that a pattern can be formed with a thin resist.
However, when the hard mask, the organosiloxane-based thin film and the photoresist are removed by oxygen plasma, the low-dielectric-constant interlayer dielectric film existing under the organosiloxane-based thin film may be exposed to oxygen plasma or the like and damaged. For example, in the case of pattern formation by a via-first dual damascene process, when the organosiloxane-based thin film filled in a via portion is removed by oxygen plasma, the low-dielectric-constant interlayer dielectric film around the via portion is damaged, causing the problem of significant degradation of electrical characteristics. Meanwhile, in the process of removing the hard mask and the organosiloxane-based thin film, since dry etching residue adheres to the wafer, it is required to remove the dry etching residue simultaneously. Accordingly, in the production of semiconductor elements in which the low-dielectric-constant interlayer dielectric film is used, a method, in which the hard mask, the organosiloxane-based thin film and the photoresist are removed at a level equal to that of the oxygen plasma process while suppressing damage to the low-dielectric-constant interlayer dielectric film, the copper, the barrier metal and the barrier dielectric film, and in which dry etching residue is removed simultaneously, is desired.
Recently, use of a fluorocarbon-based gas in dry etching has become popular, and therefore, fluorine is contained in dry etching residue. For this reason, fluorine is mixed into the cleaning liquid in the process of removing the dry etching residue. Fluorine seriously damages the low-dielectric-constant interlayer dielectric film and the copper particularly when the pH becomes acidic. However, even when the pH of the cleaning liquid was not acidic, there was a case where serious damage to the low-dielectric-constant interlayer dielectric film and the copper was observed when cleaning the semiconductor element with the cleaning liquid after use for removal of dry etching residue. The cause for the damage is not clear, but it is expected that a part of dry etching residue becomes an acid such as H2SiF6 as in the case of dissolving SiO2 with HF when subjecting the low-dielectric-constant interlayer dielectric film containing Si or O to dry etching with the fluorocarbon-based gas. Since fluorine also exists on the semiconductor element because of the influence of dry etching gas, it is considered that hydrofluoric acid is locally formed during cleaning with the cleaning liquid, causing damage to the low-dielectric-constant interlayer dielectric film and the copper. Therefore, a method for cleaning a semiconductor element, in which the low-dielectric-constant interlayer dielectric film and the copper are not damaged even when dry etching residue is mixed into the cleaning liquid, is desired.
For a hard mask, titanium or titanium nitride may be used. In this case, when the hard mask is removed with a cleaning liquid, titanium gets mixed with the cleaning liquid. In the case of a cleaning liquid containing hydrogen peroxide, when titanium is mixed therewith, decomposition of hydrogen peroxide is accelerated to worsen the preservation stability of the cleaning liquid. Therefore, a method for suppressing decomposition of hydrogen peroxide caused by titanium which gets mixed with the cleaning liquid is desired.
Patent Document 1 proposes a method for cleaning semiconductor elements with a cleaning liquid comprising hydrogen peroxide, amino polymethylene phosphonic acids, potassium hydroxide and water.
Patent Document 2 proposes a cleaning liquid that is a liquid for treating wiring substrates, which comprises hydrogen peroxide, quaternary ammonium hydroxide and an anticorrosive of tungsten and has a pH of 7 to 10, wherein the anticorrosive of tungsten is at least one selected from the group consisting of quaternary ammonium and a salt thereof, quaternary pyridinium and a salt thereof, quaternary bipyridinium and a salt thereof and quaternary imidazolium and a salt thereof.
Patent Document 3 proposes a titanium nitride removing liquid which comprises 10 to 40% by mass of hydrogen peroxide and tetraalkylammonium hydroxide and has a pH of 6.0 to 8.2 at 25° C.
Patent Document 4 proposes a cleaning liquid for semiconductor devices which comprises an oxidant, a metal etching agent and a surfactant and has a pH of 10 to 14.
Patent Document 5 proposes a polyester produced using a titanium complex compound as the main catalyst, and as a chelating agent of the titanium complex compound, the document mentions hydroxy polycarboxylic acid and/or nitrogen-containing polycarboxylic acid.